全文获取类型
收费全文 | 12136篇 |
免费 | 1083篇 |
国内免费 | 1379篇 |
专业分类
化学 | 3755篇 |
晶体学 | 55篇 |
力学 | 1113篇 |
综合类 | 173篇 |
数学 | 6423篇 |
物理学 | 3079篇 |
出版年
2024年 | 19篇 |
2023年 | 136篇 |
2022年 | 221篇 |
2021年 | 284篇 |
2020年 | 310篇 |
2019年 | 359篇 |
2018年 | 336篇 |
2017年 | 384篇 |
2016年 | 288篇 |
2015年 | 299篇 |
2014年 | 500篇 |
2013年 | 1197篇 |
2012年 | 504篇 |
2011年 | 636篇 |
2010年 | 512篇 |
2009年 | 671篇 |
2008年 | 721篇 |
2007年 | 883篇 |
2006年 | 690篇 |
2005年 | 664篇 |
2004年 | 565篇 |
2003年 | 596篇 |
2002年 | 516篇 |
2001年 | 432篇 |
2000年 | 408篇 |
1999年 | 403篇 |
1998年 | 357篇 |
1997年 | 314篇 |
1996年 | 243篇 |
1995年 | 165篇 |
1994年 | 167篇 |
1993年 | 116篇 |
1992年 | 95篇 |
1991年 | 81篇 |
1990年 | 63篇 |
1989年 | 67篇 |
1988年 | 61篇 |
1987年 | 61篇 |
1986年 | 36篇 |
1985年 | 49篇 |
1984年 | 31篇 |
1983年 | 18篇 |
1982年 | 29篇 |
1981年 | 27篇 |
1980年 | 13篇 |
1979年 | 14篇 |
1978年 | 16篇 |
1977年 | 13篇 |
1976年 | 7篇 |
1973年 | 5篇 |
排序方式: 共有10000条查询结果,搜索用时 15 毫秒
191.
Mao-fengZhang Qiao-hongYao Chun-huiHuang Wei-xiaoCao 《高分子科学》2005,(1):27-27
A kind of azo-containing resin (Azo-R) was synthesized by a simple way through the coupling reaction of 2-nitro-N-methyldiphenylamine-4-diazoresin (NDR) with phenol, and a new covalentely attached multilayer film from Azo-R as H-donor and photosensitive diazoresin, diphenylamine-4-diazoresin (DR) as H-acceptor via H-bonding attraction by selfassembly technique has been fabricated. Following the decomposition of diazonium group of DR under exposure to UV light, the H-bonds between the layers of the film convert to covalent bonds and the film becomes very stable toward polar solvents or electrolyte aqueous solutions. Thus the UV-irradiated azo-containing films can be used to measure photocurrent in a conventional three-electrode photoelectrochemical cell using KCl as supporting electrolyte. It was confirmed that the azo-containing multilayer film is responsible for the photocurrent generation. 相似文献
192.
The binding of sodium dodecyl benzene sulphonate (SDBS) with poly(N-vinyl-2-pyrrolidone) (PVP) has been investigated at 303.15 and 313.15 K using equilibrium dialysis, surface tension, viscosity, ultrasound velocity and ultrasound absorption techniques. From each of these studies four distinct regions of SDBS-PVP interactions were observed. Interaction of SDBS with PVP was found to involve the binding of surfactant dimers with the polymer molecule followed by usual micellization. The binding data has been analyzed in terms of various models of polymer-surfactant interaction. 相似文献
193.
Barbara Dogan Hans-Dieter Beckhaus Hermann Birkhofer Christoph Rüchardt 《欧洲无机化学杂志》1990,123(6):1365-1368
Effects of Substituents on the Strength of C - C Bonds, 81. - Heats of Formation and Strain of 1,1,2,2-Tetraethylethylene Glycol Dimethyl Ether and D,L .-1,2-Dimethyl-l,2-diphenylethylene Glycol Dimethyl Ether The heats of combustion of the title compounds 1 and 2 were measured calorimetrically with the result (kcal mol -1, s. d. in parentheses) ΔH°c = − 1880.1 (± 0.6) and − 2373.3 (± 1.4). The heat of vaporisation of 1 ΔHv = 14.3 (± 0.3) and the heat of sublimation of 2 ΔHsub = 27.2 (± 0.5) were derived from their temperature dependance of the vapor pressure. The latter were determined between 30 and 80°C using a flow method. The resulting standard heats of formation ΔH°t(g) = −122.4 (± 0.7) and −43.8 (±1.5) for 1 and 2 correspond to a strain enthalpy (s) of 15.9 and 8.0 kcal mol-1, respectively. The steric strain of the dimethoxyethanes 1 and 2 is about one fourth lower than the strain of the corresponding dimethylethanes 3 and 4 bearing the same substituents. Thus, a methoxy group causes less steric stress than a methyl group. 相似文献
194.
Ken-Ichi Ito Masamichi Nishimura Minoru Sashio Masahiro Tsunooka 《Journal of polymer science. Part A, Polymer chemistry》1994,32(11):2177-2185
It was found that amines were formed efficiently by the photolysis of O-acyloximes followed by hydrolysis in polystyrene films and the relationship between structures of O-acyloximes and yields of amines were investigated. O-phenylacetyl acetophenone oxime (PaApO), O-pivaloyl acetophenone oxime (PApO), and O-benzoyl acetophenone oxime (BApO) as monofunctional O-acyloximes and O,O′-succinyl diacetophenone oxime (SDApO) and O,O′-glutaryl diacetophenone oxime (GDApO) as bifunctional O-acyloximes were examined. The yields of amines for PaApO and SDApO under N2 were ca. 70%, which was the highest among O-acyloximes examined in this experiment. On the other hand, the yields for PApO, BApO, and GDApO were less than 15% and it was verified that the hydrogen abstraction by imino radicals via 6-membered cyclic intermediates resulted in the lowering of yields. Although the effect of oxygen under photolysis on the yields of amine for PaApO was negligible under 50% conversion of PaApO, the yield decreased with further increase in the conversion and was 50% at 90% conversion. © 1994 John Wiley & Sons, Inc. 相似文献
195.
V. P. Korolev 《Journal of Structural Chemistry》2006,47(6):1084-1090
A new equation is suggested to define the temperature dependence of the Gibbs energy of hydration of hydrophobic substances: ΔG 0 = b 0 + b 1 T + b 2lnT. According to this equation, the hydration heat capacity is in inverse proportion to temperature. Consistent values of hydration heat capacity of nonpolar solutes have been obtained for different temperatures using data on solubility and dissolution enthalpy. The contributions of the hydrocarbon radicals and OH group to the heat capacity of hydration of the compounds were found for the temperature range 248–373 K. The hydration heat capacity of the hydroxyl group has a weak dependence on temperature and increases by only 12 J/(mol·K) in the specified temperature interval. Changes in the hydration entropy of hydrophobic and OH groups are calculated for the temperature increasing from 248 K to 373 K. 相似文献
196.
O. M. Radul M. Z. Krimer O. N. Rebrova V. N. Biyushkin I. V. Feofanova A. A. Panasenko 《Russian Chemical Bulletin》1993,42(3):522-527
The rearrangement of enol acylates of aryl 1H-1, 2, 4-triazol-1-ylmethyl ketones at 140–150°C in acetic anhydride is studied. The migration of the acyl group to the C(5) atom of the heterocycle is found to be intramolecular. The characteristics of the original and final products are presented. X-ray structural studies of the enol acetates of 2, 4-dichlorophenyl 1H-1, 2, 4-triazol-1-ylmethyl ketone and 2, 4-dichlorophenyl 5-acetyl-1H-1, 2, 4-triazol-1-ylmethyl ketone are carried out.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 560–564, March, 1993. 相似文献
197.
H. Binder B. Kohlstrunk U. Brenn W. Schwieger G. Klose 《Colloid and polymer science》1998,276(12):1098-1109
Microcrystals of the metal silicate hydrate ilerite orient macroscopically on the surface of a ATR-crystals and thus, are
accessible for infrared linear dichroism measurements. We present first results which indicate that the alkyl chain packing
and the orientation of the polar group of dodecyltrimethylammoniumbromide (DTAB) intercalated between silicate layers can
be determined in terms of infrared order parameters. The properties of DTAB can be modulated by the relative humidity of the
surrounding atmosphere and by temperature. Upon heating DTAB undergoes a phase transition from a paraffin-like solid to a
fluid phase. The former is characterized by the orthorhombic perpendicular packing of the frozen alkyl chains with tilted
long axes. The interactions between the ionic groups of the surfactant and that of the host matrix stabilize the lamellar
arrangement of DTAB in the crystalline and in the fluid phases.
Received: 14 January 1998 Accepted: 27 July 1998 相似文献
198.
The 2-(diphenylphosphino) ethyl group (DPPE) as a new carboxyl-protecting group in peptide chemistry
Dominique Chantreux Jean-Paul Gamet Robert Jacquier Jean Verducci 《Tetrahedron》1984,40(16):3087-3094
The use of the 2-(diphenylphosphino)ethyl group for carboxyl-protection of amino acids or peptides is described. This group is easily introduced by esterification using 2-(diphenylphosphino) ethanol in the presence of dicyclohexylcarbodiimide and 4-(dimethylamino)pyridine. These Dppe esters are stable under the standard conditions for peptide synthesis. Deprotection is carried out under mild conditions by quaternisation using methyl iodide followed by a β-elimination induced by fluoride ion or potassium carbonate. 相似文献
199.
Olivier Busnel 《Tetrahedron letters》2007,48(33):5767-5770
The preparation of new Nβ-Fmoc-protected aza-β3-amino acids (aza-β3-aa) with proteinogenic side chains as well as their Nβ-Fmoc, Nβ-Cbz or Nβ-Boc aza-β3-amino esters (from Pro, Asn, Asp, Glu, Gln) by successive nucleophilic substitutions will be described. 相似文献
200.
Kosuke Katagiri Yukina Yamamoto Yuui Takahata Ryoga Kishibe Naoki Fujimoto 《Tetrahedron letters》2019,60(30):2026-2029
Anthracenyl(diphenyl)phosphine oxide and dianthracenylphenylphosphine oxide as photoactive compounds have been synthesized. Anthracenyl group of these compounds indicate the multi-functional roles such as an emission component, a photodimerization component, and a leaving group. When the light irradiation was performed under an oxygen atmosphere, photo-oxidative PC bond cleavage to leave the antharacenyl group was observed. Moreover, phosphonyl radical was produced and then PP bond formation to form diphosphane was observed. 相似文献